Elusive but Ubiquitous Microbe Fingered as Gum Disease Culprit in Stanford Study.

News Editors & Health/Medical Writers

STANFORD, Calif.--(BUSINESS WIRE)--April 22, 2004

Even biology majors may not have heard much about archaea. Along with bacteria and eukarya (which encompass every organism from fungi to mammals), the elusive microbes make up one of the

"It's not surprising that no one has really heard about them; archaea have still not even penetrated mainstream biology textbooks," said David Relman, MD, associate professor of medicine (infectious diseases) and of microbiology and immunology. There are, however, at least as many of them as there are bacteria," he said.

Archaea look a lot like bacteria, but appearances can be deceiving. Genetically and biochemically they are as different from bacteria as bacteria are from humans. The microbes live in many extreme environments -- from hot springs to salt lakes to submarine volcanoes -- but also within animals, including the human colon, vagina and mouth.

"To me it is one of those fundamental puzzles: they are everywhere and, given that we must be exposed to them somewhat frequently, if not all the time, why is it that we can't name one disease-causing member of this enormous domain?" Relman wondered. He and his group at the Veterans Affairs Palo Alto Health Care System have shown a never-before-known connection between the abundance of archaea and the severity of a human gum disease called periodontitis.

Chronic periodontitis, which affects about one-third of Americans, may result in tooth loss and is thought to play a role in a range of conditions including atherosclerosis, stroke and early delivery of low birth-weight infants. While there is a general consensus that bacteria play a role in gum disease, no single microbe has been implicated as the culprit.

Relman and members of his lab embarked on a comprehensive, controlled study of the archaea found in the subgingival crevice -- the deep gap between the gums and teeth -- where periodontitis begins. They rigorously analyzed samples from 58 patients' mouths taken by their collaborator, Gary Armitage, DDS, at the UC-San Francisco School of Dentistry, and found that more than one-third of the periodontitis patients had archaea in their diseased subgingival spaces, but nowhere else in their mouths. In addition, the relative abundance of archaea correlated with disease severity. Their findings are published in this week's issue of the Proceedings of the National Academy of Sciences.